General questions about apps

Hello,

I am exploring Akounting for now and have installed on a local server for testing purposes.

I have a question regarding the app store? For my use case, I am interested in on-premise app (and not the cloud ones).

1) When buying an app what do we get? A zip archive to be downloaded and installed? Access to git private repository?

2) Assuming we take the yearly subscription price. What happens after a year if we don't renew the subscription. The app / module is becoming inactive / unusable? or is it just the app update that is disabled?

3) Is it a way to test the app before buying?

4) side question: as a developer, is it possible to collaborate / make contributions to an app? It depends on the author, I guess.